1. Field of the Invention
The present invention relates to a novel jet mill, a process for generating fine particles by means of a jet mill, a process for simultaneous surface modification of the fine particles and also the products produced by this process.
2. Description of the Related Art
In milling operations performed by means of jet mills, the material to be milled and/or to be classified comprises relatively coarse and relatively fine particles, which are entrained in an air stream and form the product stream, which can be introduced into a housing of an air classifier of the jet mill. The product stream passes in the radial direction into a classifying wheel of the air classifier. In the classifying wheel, the relatively coarse particles are separated from the air stream and the air stream leaves the classifying wheel with the fine particles axially through an outflow pipe. The air stream with the fine particles to be filtered out or to be produced may then be fed to a filter, in which a fluid, such as for example air, and fine particles are separated from one another.
DE 198 24 062 A1 discloses such a jet mill, in the milling chamber of which furthermore at least one high-energy milling jet of hot steam is introduced with high flow energy, the milling chamber having in addition to the inlet device for the at least one milling jet an inlet for the material for milling and an outlet for the product, and, in the region where the material for milling and at least one milling jet of hot steam come together, and material for milling have at least approximately the same temperature.
Furthermore, a corresponding air classifier, in particular for a jet mill, is disclosed for example by EP 0 472 930 B1. This air classifier and the way in which it operates are extremely satisfactory in principle.
The aforementioned processes have the disadvantage that they can only be operated with great expenditure on apparatus and, moreover, are very energy-intensive. In order to minimize this problem, DE 10 2006 023 193 proposes a process in which the milling pressure is lowered below 4.5 bar. This process is more energy-efficient, but has the disadvantage that, as before, there are high temperatures of the operating medium (milling gas). For generating the pressure of the operating medium and the temperature of the operating medium, DE 10 2006 023 193 refers, for example, to DE 198 24 062 or proposes the use of a compressor.
As an alternative to jet mills, the use of mechanical or classifying mechanical mills is known. However, these mills have the disadvantage that the material for milling causes great abrasion on the mill as a result of the direct contact with the rotor/stator. This in turn leads to high maintenance costs for the mill, but at the same time also to undesired contamination of the material from milling.